As the detector for a gas chromatograph, various types of detectors have conventionally been proposed and practically applied, such as a thermal conductivity detector (TCD), electron capture detector (ECD), flame ionization detector (FID), flame photometric detector (FPD) and flame thermionic detector (FTD). Among those detectors, the FID is most widely used, particularly for the purpose of detecting organic substances. The FID is a device that ionizes sample components in a sample gas by hydrogen flame and detects the resultant ion current. It can attain a high dynamic range of approximately six-digit levels.
However, the FID has the following drawbacks: (1) Its ionization efficiency is low, so that its minimum detectable amount is not sufficiently low. (2) Its ionization efficiency for alcohols, aromatic substances and chlorine substances is low. (3) It requires hydrogen, which is a highly hazardous substance; therefore, an explosion-proof apparatus or similar kind of special equipment must be provided, which makes the entire system more difficult to operate.
On the other hand, as a detector capable of detecting various compounds from inorganic substances to low-boiling organic compounds, a pulsed discharge detector (PDD) has conventionally been known (for example, refer to Patent Document 1) and practically used (for example, refer to Non-Patent Document 1). In the pulsed discharge detector, the molecules of helium or another substance are excited by a high-voltage pulsed discharge. When those molecules return from the excited state to the ground state, they generate an optical energy. This optical energy is utilized to ionize a molecule to be analyzed. An ion current produced by the generated ions is detected to obtain a detection signal corresponding to the amount (concentration) of the molecule to be analyzed.
In most cases, the pulsed discharge detector can attain higher ionization efficiencies than the flame ionization detector (FID). For example, the ionization efficiency of the FID for propane is as low as 0.0005 [%], whereas the pulsed discharge detector has achieved a level as high as 0.07 [%]. Despite this advantage, the dynamic range of the pulsed discharge detector is not as high as that of the FID; the fact is that the former is one or more digits lower than the latter. This is one of the reasons why the pulsed discharge detector is not as widely used as the FID.
Patent Document 1: Specification of U.S. Pat. No. 5,394,092
Patent Document 2: Specification of U.S. Pat. No. 5,892,364
Non-Patent Document 1: “Muki-Gas Bunseki Ha ppb No Ryouiki He; PPD Koukando Bunseki Shisutemu (For Inorganic Gas Analysis at ppb Levels; PPD High-Sensitivity Analysis System)”, [online], Shimadzu Corporation, [searched on Feb. 29, 2008], Internet <URL: http://www.an.shimadzu.co.jp/products/gc/pdd.htm>
Non-Patent Document 2: M. Teschke et al., “High-Speed Photographs of a Dielectric Barrier Atmospheric Pressure Plasma Jet”, IEEE Transaction on Plasma Science, Vol. 33, No, 2, April 2005, pp. 310-311
Non-Patent Document 3: R. Gras et al., “Gas Chromatographic Applications with the Dielectric Barrier Discharge Detector”, Journal of Chromatographic Science, Vol. 44, February 2006
Non-Patent Document 4: P. Bocek et al., “Flame Ionisation Detection”, Chromatographic Reviews, 15(1971), pp. 111-150
Non-Patent Document 5: K. Nishikawa and H. Nojima, “Airborne Viruses inactivation with Cluster Ions Generated in a Discharge Plasma”, Sharp Gihou, No. 86, August 2003, pp. 10-15
Non-Patent Document 6: The Institute of Electrostatics Japan, ed., Seidenki Hando-Bukku (Electrostatics Handbook), Ohm-sha (Tokyo), Nov. 2006, pp. 213-214